Main.java Source code

Introduction

Here is the source code for Main.java

Source

//package com.java2s;
import java.util.Map;
import java.util.TreeMap;
import java.util.HashMap;

import java.util.function.BinaryOperator;
import java.util.function.Function;
import java.util.stream.Collector;
import java.util.stream.Collectors;

public class Main {
    public static <T, K, U> Collector<T, ?, TreeMap<K, U>> toTreeMap(Function<? super T, ? extends K> keyMapper,
            Function<? super T, ? extends U> valueMapper) {
        return Collectors.toMap(keyMapper, valueMapper, throwingMerger(), TreeMap::new);
    }

    public static <T, K, U> Collector<T, ?, Map<K, U>> toMap(Function<? super T, ? extends K> keyMapper,
            Function<? super T, ? extends U> valueMapper) {
        return Collectors.toMap(keyMapper, valueMapper, throwingMerger(), HashMap::new);
    }

    /**
     * Returns a merge function, suitable for use in
     * {@link Map#merge(Object, Object, BiFunction) Map.merge()} or
     * {@link #toMap(Function, Function, BinaryOperator) toMap()}, which always
     * throws {@code IllegalStateException}. This can be used to enforce the
     * assumption that the elements being collected are distinct.
     *
     * @param <T>
     *            the type of input arguments to the merge function
     * @return a merge function which always throw {@code IllegalStateException}
     */
    private static <T> BinaryOperator<T> throwingMerger() {
        return (u, v) -> {
            throw new IllegalStateException(String.format("Duplicate key %s", u));
        };
    }
}